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Melilite refers to a mineral of the melilite group. Minerals of the group are solid solutions of several endmembers, the most important of which are gehlenite and åkermanite. A generalized formula for common melilite is (Ca,Na)2(Al,Mg,Fe2+)(HREF="http://www.kotoba.ne.jp/word/11/Aluminium" TITLE="Aluminium">Al,Si)SiO7 ). Discovered in 1793 near Rome, it has a yellowish, greenish brown color. The name derives from the Greek words meli (μέλι) "honey" and lithos (λίθους) "stone". Minerals of the melilite group are sorosilicates. They have the same basic structure, of general formula ''A''2''B(T''2O7). The melilite structure consist of pairs of fused ''T''O4, where ''T'' may be Si, Al, B, in bow-tie form. Sharing one corner, the formula of the pair is ''T''2O7. These bow-ties are linked together into sheets by the ''B'' cations. The sheets are held together by the ''A'' cations, most commonly calcium and sodium. Aluminium may sit on either the ''T'' or the ''B'' site. Minerals with the melilite structure may show a cleavage parallel to the (001) crystallographic directions and may show weaker cleavage perpendicular to this, in the directions. Melilite is tetragonal. The important endmembers of common melilite are åkermanite Ca2Mg(Si2O7) and gehlenite Ca2Al(). Many melilites also contain appreciable iron and sodium. Some other compositions with the melilite structure include: alumoåkermanite (Ca,Na)2(Al,Mg,Fe2+)(Si2O7), okayamalite Ca2B(), gugiaite Ca2Be(), hardystonite Ca2Zn(), barylite BaBe2(), andremeyerite BaFe2+2(). Some structures formed by replacing one oxygen by F or OH: leucophanite (Ca,Na)2(Be,Al)(), jeffreyite 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Melilite」の詳細全文を読む スポンサード リンク
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